What are signs of a controlling would/could be romantic partner ?

Situations while beginning to date.

Obvious example would be on where to go.
Controlling person will insist on their choice(s).

Yet this can also be seen on how they behave around their friends even family.

Note a controller may very well have no family. Yet they usually do have friends.

Problem comes when they have neither. They maybe just be loners. Not necessarily controllers. Then see how they behave around your friends and family. A controller will hate that. A loner not necessarily. Loners usually attempt to go along.

Unfortunately, not something you'll easily see in the beginning.
It will be a subtle shift.
They will make you feel guilty or bad for doing something they don't want you to. And it will seem like your idea that you've ditched that thing for them.
All your plans will have to include them.
Subtle jealousies that will make you feel bad and you begin giving up on your friends and even family.

That kind of thing.

Oh boy ...